EFFECTS OF TANK MIXES OF ROUNDUP WITH FUNGICIDES AND INSECTICIDES ON ROUNDUP READY SOYBEANS

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1 EFFECTS OF TANK MIXES OF ROUNDUP WITH FUNGICIDES AND INSECTICIDES ON ROUNDUP READY SOYBEANS Jarrod T. Hardke, Gus M. Lorenz, Adam Chappell, Craig Shelton University of Arkansas Cooperative Extension Service, Little Rock, AR ABSTRACT Field experiments were conducted in 2004 at a single location in Arkansas to evaluate potential weed control interactions when Roundup WeatherMax was applied with several insecticides and fungicides. No treatments significantly differed from the treatment of Roundup WeatherMax alone. However, several treatments did differ significantly from one another. Roundup WeatherMax alone was rated at 86.67% control. The highest rating was observed when Roundup WeatherMax was applied with Stratego, with a rating of 98.33% control, followed closely by WeatherMax applied with Stratego + Lorsban, with a rating of 95.00% control. Tilt, Quadris, Folicur, Lorsban, Asana XL, and Quadris + Karate Z in combination with Roundup WeatherMax controlled weeds 14 DAT no more than 91.67% and no less than 86.67% control, which was less than when WeatherMax was applied with Stratego and Stratego + Lorsban, but greater than or equal to the rating of WeatherMax applied alone. The lowest control rating was observed when Roundup WeatherMax was tank mixed with Karate Z, (80.00% control) and with Headline + Asana XL (78.33% control) at 14 DAT when compared with Roundup WeatherMax applied alone (86.67% control). INTRODUCTION During the 2003 growing season, an estimated 86% (2.5 million acres) of the total soybean crop were Roundup Ready. The estimate percent yield loss due to weed competition is 5% at 15 days after emergence, 15% at 30 days after emergence, and 30% at 45 days after emergence (Tingle, 2004). Currently in Arkansas soybeans, Roundup is used in preplant-foliage situations for annual grasses and broadleaf weeds. It is also used in postemergence over-the-top applications for the control of emerged annual grasses, Johnsongrass, red rice, cocklebur, sicklepod, pigweed, morningglories, prickly sida, velvetleaf, eclipta, spurge, hemp sesbania, northern jointvetch, and smartweed. Additionally, Roundup is used preharvest for the desiccation of green weed foliage, as a spot treatment to control johnsongrass and bermudagrass and for postemergence johnsongrass wipe-on (Scott, 2004). RESEARCH PROBLEM Various pesticides were tank-mixed with glyphosate to determine the positive and/or negative effects of such a mix. The purpose of this experiment was to test the effectiveness of Roundup WeatherMax when mixed in a tank with various pesticides for disease and insect control.

2 Roundup WeatherMax was tested at a rate of lb ae/a for efficacy against a considerable weed population. Aside from this individual treatment of Roundup WeatherMax, WeatherMax was also tank-mixed with various pesticides to determine the potential for crop injury and losses of weed control. Roundup WeatherMax was tankmixed with Stratego 22.8% EC, Tilt 41.8% EC, Quadris 2.08 FS, Folicur 38.7% SC, Headline 23.6% EC,,,, Quadris 2.08 FS +, Headline 23.6% EC +, and Methyl Parathion 4 EC. MATERIALS AND METHODS The Roundup Ready cotton trial was conducted at Hardke Farms at Carlisle, Arkansas in Prairie County in Asgrow A5501 RR was planted on 1 June. The field was planted and afterwards subdivided into plots of 4 rows on 30 inch spacing and 20 feet in length. Plots were set up in a randomized complete block with three replications. Treatments were made according to statewide threshold recommendation. Treatments were applied with a CO 2 backpack applicator using a 4 row boom with 19 inch nozzle spacing. The nozzles used for application were Tee-Jet TXVS 6. Operating pressure was 45 pounds per square inch and gallons per acre of volume. Treatments included Roundup WeatherMax ( lb ai/a) alone and Roundup WeatherMax ( lb ai/a) tank mixed with each of the following fungicides and insecticides: Stratego 22.8% EC at qt/a, Tilt 41.8% EC at qt/a, Quadris 2.08 FS at qt/a, Folicur 38.7% SC at 0.25 qt/a, Headline 23.6% EC at 0.25 qt/a, Karate Z 2.08 CS at lb ai/a, at 0.5 lb ai/a, at 0.3 qt/a, Quadris 2.08 FS at qt/a + Karate Z 2.08 CS at lb ai/a, Headline 23.6% EC at 0.25 qt/a + Asana XL 0.66 EC at 0.3 qt/a, Stratego 22.8% EC at qt/a + at 0.5 lb ai/a, and Methyl Parathion 4 EC at 0.5 lb ai/a. Weed control was visually rated on a scale of 0 to 100% where 0 = no control and 100 = all weeds dead as compared with a non-treated check. The single treatment was foliar applied on 18 June. A single observation was conducted on 2 July at 14 DAT. Data were analyzed using Agricultural Research Manager version 7 using Analysis of Variance and LSD (P=0.10) RESULTS AND DISCUSSION The lb ae/a rate of Roundup showed a rating of at 14 days after treatment. Weed control ranged from 78.33% to 98.33% at 14 days after treatment. Observing herbicide efficacy, Stratego showed the highest weed control on a percentage basis with a rating of 98.33%. Similar numbers were found in several of the other tank mixes. Roundup WeatherMax tank mixed with Stratego qt/a + Lorsban 0.5 qt/a showed a rating of 95.00% control at 14 days after treatment. In addition, Roundup WeatherMax tank mixed with each of the following showed a higher weed control rating than that of Roundup WeatherMax applied alone: Quadris at qt/a (91.67% control), Tilt at qt/a (90.00% control), Asana XL at 0.3 qt/a (90.00% control), Quadris at Karate Z at lb ai/a (90.00% control), and Lorsban at 0.5 qt/a (88.33% control). 2

3 Roundup WeatherMax tank mixed with Headline 0.25 qt/a + Asana XL 0.3 qt/a showed the lowest rating at 14 days after treatment with a rating of Also, Roundup WeatherMax tank mixed with Karate Z lb ai/a (80.00%) and Headline 0.25 qt/a (81.67%) showed decreased control from that of Roundup WeatherMax alone, (86.67%). Folicur 0.25 qt/a showed no change in weed control with a rating of 86.67%, equivalent to the rating of when Roundup WeatherMax was applied alone, (86.67%). PRACTICAL APPLICATION The insecticides tank-mixed with Roundup WeatherMax in this study showed no significant difference in the weed control effectiveness of Roundup. In some cases, the insecticide and/or fungicide caused the Roundup activity to be faster, and in some it caused it to be slower. In regard to phytonecrosis rated on the soybeans, none of the applications showed a significant difference from that of Roundup alone at 14 DAT. This test called for weed control and phytonecrosis ratings at both 7 and 14 days after treatment. However, the ratings taken at 7 days after treatment were taken incorrectly, and were therefore disregarded in this study. ACKOWLEDGEMENTS I would like to thank Dr. Gus M. Lorenz, III, for all of his help and recommendations. I would also like to thank Adam Chappell and Blaire Griffin for their help with evaluations, and Craig Shelton for his help with application. REFERENCES Tingle, Chris, Dwayne Beaty, and Trey Reaper Early-Season Weed Control with Glyphosate Applications. University of Arkansas Cooperative Extension Service Soybean Notes, Scott, R.C., J.W. Boyd, and K.L. Smith, et. al Recommended Chemicals for Weed and Brush Control, MP-44 Arkansas, University of Arkansas Cooperative Extension Service. 3

4 Table 1. Weed Control Ratings of Roundup WeatherMax alone and tank-mixed with insecticides and fungicides Application Date: 18 June Evaluation Date: 2 July (14 DAT) Evaluation Method: Ratings based on a scale of 0-100% weed control Treatment and Rate Rate Lb ai/a Weed Control 14 DAT Roundup WeatherMax abc Stratego 22.8% EC a Tilt 41.8% EC abc Quadris 2.08 FS abc Folicur 38.7% SC abc Headline 23.6% EC bc c abc abc Quadris 2.08 FS abc Headline 23.6% EC + Stratego 22.8% EC + Methyl Parathion 4 EC c ab abc Means followed by same letter do not significantly differ (P=.10, Duncan's New MRT) 4

5 Table 2. Phytonecrosis observed on crop Application Date: 18 June Evaluation Date: 2 July Evaluation Method: Ratings based on a scale of 0-100% necrosis Treatment and Rate Rate Lb ai/a Phytonecrosis 14 DAT Roundup WeatherMax ab Stratego 22.8% EC ab Tilt 41.8% EC ab Quadris 2.08 FS a Folicur 38.7% SC a Headline 23.6% EC a a ab Quadris 2.08 FS + Headline 23.6% EC + Stratego 22.8% EC + Methyl Parathion 4 EC ab ab a ab ab Means followed by same letter do not significantly differ (P=.05, Duncan's New MRT) 5